Band-pass filter



June 9, 1959 H,s|MONs i 2,890,423

BAND-PASS FILTER Filed July 21, 1954 INVENTOR HENDRIK SIMON S AGENT United States Patent O BAN D-PASS FILTER Hendrik Simons, Eindhoven, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Deia ware Application July 21, 1954, Serial No. 444,695 Claims priority, application Netherlands August 13, 1953 3 Claims. (Cl. 333-78) The invention relates to an electrical assembly such as a bandepass filter comprising substantially two coils provided with adjustable ferromagnetic cores arranged on an insulating foot or base provided with terminals or soldering tags so that the coil axes are at right angles to this base, and several substantially rod-shaped ferromagnetic parts which are arranged around the coils and parallel to them in order to reduce their stray eld.

The space taken up `by such a band-pass lilter on the usually horizontal frame on which it is mounted is determined by the horizontal dimensions of the conductive housing or metal can required to screen the lilter. Owing to the reduced stray lield of the coils these dimensions may be small, since the screening can may surround the coils with a small amount of intermediate space and, in addition, the coils may `be closely adjacent without the coupling becoming excessive. Consequently the said dimensions may be a minimum, for example, 12 x 25 mm. A further advantage of the described arrangement consists in that it permits the adjustment of the ferromagnetic core provided in the coils, which usually is movable vertically for controlling the inductance, to be effected from above.

However, the attachment of the various parts of the base presents difficulty. This attachment must satisfy certain mechanical requirements, since, when the core is adjusted, for example, by means of a screw driver, comparatively strong forces may be exerted on the long thin coil former. in addition, the attachment must satisfy electrical requirements with respect to the insulation resistance between the closely adjacent primary and secondary coil, since these usually are connected to an anode supply and the grid of an amplifier tube respectively.

According to the invention the said diculty is solved in that the coils together with the associated ferromagnetic parts are secured to an insulating supporting wall which is arranged at right angles to the base, passes between the coils and partially surrounds them. In this event the coils may be firmly nestled to and partially on Vthe supporting wall, which may be S-shaped and have mating recesses `formed in it, and the length oi the leakage resistance path along the surface of the supporting wall is considerable in spite of the small direct spacing between the coils.

The accompanying drawing shows an embodiment ol` a band-pass lter according to the invention, in which Fig. l is an elevational view with the screening can removed in i'ront to show the interior, and Fig. 2 is a crosssectional view along the line ll-ll in Fig. l.

The frame of the band-pass lter shown in the drawing is constituted by an insulating moulding, eg. of a su ible phenolic woodilonr-lled moulding material, comprising a base part 1 arranged so as to be parallel to tire usually horizontal frame wall 3 (such a chassis) on which the band-pass filter is mounted, an upstanding, supporting wall 5 at right angles to the base horizontal cross-section of which (see Fig. 2) is substantially S-shaped, and a depending part 9 projecting below the base 1, which part lCC 9 is provided with downwardly extending connecting tags or terminal members 7 and passes through an aperture provided in the frame plate 3.

The two coils of the band-pass filter (see Fig. 1) each consist of a winding 11 Wound on a thin coil former 13 lhaving a diameter of, for example, 2 mms. and being provided at its top with an internal screw thread. Internally of the coil former 13 a core 15 made of soft ferromagnetic cubic ferrite is movable by means of a copper screw 16 secured to it and engaging the threaded former 13. The coil former 13 carrying the winding 11 is firmly nestled and cemented in a mating recess having a concave shape in the supporting wall 5. On either side two ferromagnetic ferrite rods 17 and 19 are secured also in mating channel-shaped recesses, through which rods the magnetic lield of the coil can largely be closed with the result that only a comparatively weak stray eld remains. A third rod 21 may `be arranged in a cavity provided in the bottom of the recess in which the coils 11, 13 is arranged (see Fig. 2).

ln a separate recess arranged on either side of the supporting wall a tubular capacitor 23 is secured, which capacitor is connected in parallel Iwith the associated coil in order to obtain the desired tuning.

A metal screening can 25, which is provided at its top with apertures through which adjusting screws 16 extend so as to project, is moved over the entire band-pass filter with the exception of the part extending below the base 1. The aggregate is secured to the frame 3 by means of a U-shaped resilient wire brace 27.

As may be seen from the preceding, the coils 11, 13 can be secured firmly to the supporting wall 5 owing to the fact that this wall surrounds the coils to some extent with the result that niches are produced in which the coils nestle. Fig. 2 shows that the electrical leakage resistance path between the coils has a considerable length due to the fact that the two coils are arranged on opposite sides of the supporting wall 5. In spite of the considerable width of the leakage resistance path, which is substantially equal to the axial length of the coil winding, the total insulation resistance of the parallel combination of the two resistances produced `by the leakage resistance paths provided between the coils is suicient even under adverse atmospheric conditions.

What is claimed is:

l. An electrical assembly comprising an insulating base i iember, metal terminal members mounted on said base member and extending substantially at right angles there to, a substantially S-shaped insulating wall member mounted on said base member and extending substantially at right angles thereto, said wall member having recesses in opposite sides thereof including opposite facing concave portions, a pair of coils each enclosing a ferromagnetic core and each seated in and secured to one of said concave portions, the axes of said coils extending substantially at right angles to said base member, a plurality of rod-shaped soft ferromagnetic members each seated in and secured to a recess in said wall member, said rod-shaped members being parallel to and arranged around the coils, a pair of capacitors mounted in recesses in said wail member on opposite sides thereof and extending parallel to said coils, means connecting said capacitors and coils to said terminal members, and a conductive housing closely surrounding said assembly.

2. An inductive assembly comprising an insulating base member, terminal members mounted on and depending from said base member, a substantially S-shaped, insulating, upstanding wall member integral with and extending substantially at right angles to said base member, said upstanding wall member having opposed, laterally-facing surfaces of extended area containing concave portions at 3. An inductive assembly comprising an insulating base member, terminal members mounted on and depending from said base member, a substantially S-shaped, insulating, `upstanding Wall member integral 'with and extending substantially at `right angles to said base member, said upstanding wall member having opposed, laterally-facing surfaces of extended area containing concave portions at opposite sides thereof so that the said concave portions lie substantially in the plane of the wall member, a pair oi coils each enclosing an adjustable ferromagnetic core secured to said Wall member each within a concave portion thereof on opposite sides and having axes also extending substantially at right angles to said base member, said wall member partially embracing each of said coils, a plurality of rod-shaped, soft ferromagnetic members arranged around and extending parallel to said coils and mounted in recesses of said Wall member, means connecting said coils to said terminal members, and a conductive can having an apertured top surrounding the insulating lbase and Wall members, said core members being adjustable within their associated coil through the apertured top of the can.

References Cited in the ile of this patent UNITED STATES PATENTS 2,458,282 Maki Jan. 4, 1949 2,544,508 Mackey Mar. 6, 1951 2,642,559 Visch l lune 16, 1953 2,722,663 Visch Nov. 1, 1955 

